I did see this link. There is no user interface locale setting DWORD in my windows 7 registry. I created the word, changed the value but could not see the locale changing to italian on restarting InDesign.
Do check comments 51 and 52 on this thread (the link that you shared, this doesn't seem to be the case for CS6)
Ah, yes, CS6 is the odd one out, I had heard that. I haven't change the UI language since CS5 by the looks of it. CS6 does have a field for a language setting:
but changing it doesn't have any effect (not that I can see, anyway). What that key does is a mystery to me. The value I see is en_US, but my CS6 installation is en_GB (which I see in the folder structure).